Histone deacetylase inhibitor CI-994 inhibits osteoclastogenesis via suppressing NF-κB and the downstream c-Fos/NFATc1 signaling pathways.

[4-(acetylamino)-N-(2-amino-phenyl) benzamide] (CI-994) is a histone deacetylase 1-3 specific inhibitor that has been shown to indirectly increase the production of Dickkopf-1, which is an inhibitor of osteoclastic development. However, whether CI-994 has an influence on receptor activator of nuclear factor-kappa B ligand (RANKL)-induced osteoclastogenesis is still unclear; in our study, this mechanism was investigated. In an in vitro study, using a tartrate-resistant acid phosphatase (TRAP) stain, an F-actin ring, bone absorption test, quantitative PCR and Western blotting, the role of CI-994 in osteoclastogenesis and the expression of related genes and proteins were investigated. In an in vivo study, the effect of CI-994 on osteolysis was evaluated using a titanium particle-induced murine calvarial osteolysis model. Our results indicated that CI-994 inhibited osteoclast differentiation and the function of bone resorption without cytotoxic effects. Moreover, CI-994 inhibited the expression of osteoclast-related genes, including ACP5, CTSK, NFATc1, c-Fos, DC-STAMP and V-ATPase-d2. Furthermore, CI-994 suppressed the phosphorylation of IκBα and p65 and the expression of downstream c-Fos and NFATc1. Consistent with the in vitro results described above, our in vivo experiment indicated that CI-994 inhibited Ti-induced osteolysis. In conclusion, CI-994 inhibited osteoclastogenesis by suppressing NF-κB and the downstream c-Fos/NFATc1 signaling pathway. Thus, this study showed the possibility of using CI-994 for the treatment of exorbitant osteoclastic bone resorption.